Release report tweaks (#2001)

[daveoconnor]

This PR is related to ticket #2001.

1. Move admin release report buttons from libraries to release report views.
2. Refined release report publishing and added locking.
3. Limited release report dropdown list.

Testing:

1. release report update docs (docs/release_reports.md) and buttons should be correct and function accordingly.
2. Publishing should be bulletproof, now has locking. More safeguards to prevent overwriting.
3. Drop down list should show dev/master, most recent release and beta, and any report configuration that doesn't have a matching version.

[gregjkal]

Great work. Love that you're continuing to move code out of libraries/forms.py.

Approved with a couple of small non-blocking suggestions.